The runaway hit about an English upper-crust family and its servants is about to begin its third season on PBS. What's in store for Lord Grantham, Lady Mary and the rest? Well ...

BERKSHIRE, England — It's a midsummer afternoon in the English countryside, and a parade of aristocrats is gliding up a grassy hill toward Downton Abbey. There is Lord Grantham, in his crisp dinner suit, followed by his daughters Lady Edith and Lady Mary. And here comes Lady Cora a few paces behind, talking on her... iPhone.

The fantasy is further shattered on closer inspection: Mary's and Edith's beaded gowns peek out from beneath white puffy coats that are distinctly 21st century. And grande dame Maggie Smith is swaddled in a robe — something the formidable Lady Violet would never countenance.

This is Highclere Castle, where the cast and crew are midway through shooting the third season of "Downton Abbey," which premieres Sunday on PBS.

Since its U.S. debut in January 2011, the English country house drama has waltzed its way into American Anglophiles' hearts and thrust PBS, which will air the series over seven Sundays this winter, into the pop cultural conversation. Affectionately spoofed by everyone from "Saturday Night Live" to Jimmy Fallon, "Downton" was nominated for 16 Emmys in 2012 (winning three) and became the most watched "Masterpiece" series on record — its Season 2 finale drew 5.4 million viewers in February 2012, the biggest in the show's history.

The series — written by Julian Fellowes and centered on the family and servants of Lord and Lady Grantham — appeals to high and lowbrows alike with its mix of doomed romance, class struggle and dry wit. The fine actors, gorgeous costumes and dazzling mansion don't hurt either.

In fact, the "Downton" spectacle is so absorbing that it's a shock to see cast members dressed as, well, themselves.

Standing outside the cluster of trailers assigned to cast and crew is Allen Leech, who plays Branson, the rebellious Irish chauffeur who lured Lady Sybil away from her family in Season 2. Wearing a gray T-shirt and jeans, Leech is full of roguish energy as he bear-hugs Michelle Dockery. She's dressed in skinny jeans and a blazer — even slimmer and paler in reality than as her blue-blooded character, Lady Mary.

Next to arrive is Dan Stevens, otherwise known as Matthew Crawley, "Downton" heir and Mary's fiance. After explaining that he's sleep deprived (his wife gave birth to their second child just two weeks before), he disappears into his trailer for a nap.

On top of producing a newborn, Stevens is also producing a movie with old friends, editing a literary magazine (thejunket.org) and planning a move to New York (he's starring in "The Heiress" on Broadway). He'd also agreed to be a judge for a prestigious literary award, the Man Booker Prize, which meant reading scores of books while running lines for the TV series.

He insists that he's not usually someone who takes on too much: "It's just a freaky year where it's all come to a head. I said yes to a few too many things. Next year will be the year of saying no." (Indeed — spoiler alert — in Britain, where the series airs months earlier than in America, viewers just learned from the Season 3 ending Christmas special that his Crawley character would not be returning for Season 4.)

Although Matthew sometimes seems bashful and understated, he serves as the linchpin of the show, which is also wildly popular in the United Kingdom. Matthew is the closest thing to a stand-in for the audience: a middle-class lawyer thrown into the lush lap of the aristocracy.

Season 3 opens in 1920. In the aftermath of World War I, the ground is shifting beneath everyone's feet. This was the era when grand families were losing their ancestral homes, unable to afford the upkeep and way of life. As the gentry's fortunes decline, Matthew's sensible work ethic becomes more crucial than ever.

Stevens looks terribly earnest in front of the cameras as he shoots a tense scene with Hugh Bonneville (Lord Grantham) in the dining room. But as soon as the director cuts, Stevens and Bonneville break into smiles and chatter.

Between scenes, Stevens bolts out of the house and plants a chair in the grass, still dressed in his formal dinner jacket. He laughs about some of the more unexpected twists and turns of the previous season. First there was the fiancee who died, leaving Matthew free to wed Lady Mary. Then there was Matthew's war injury: He was paralyzed from the waist down and then miraculously unparalyzed.

"One of the delights of the show is that you take what's thrown at you, really," he says. "Oh, he's getting out of the wheelchair? Great!"

Stevens says he was relieved that "certain references to aspects of his injury" relating to his manhood had been removed. "I'll leave it to your imagination! Because it was like, do we really need to talk about that?"